1. Field of the Invention
This invention relates to a method of obtaining improved equilibrium conditions and of simultaneously producing steam under high pressure in the production of methanol by a reaction of oxides of carbon and of hydrogen-containing gases at temperatures of 200.degree. to 300.degree. C. under a pressure of 20 to 100 bars in the presence of a copper-containing catalyst, contained within a reactor in tubes, indirectly cooled by boiling water under pressure, wherein the resulting steam is withdrawn together with circulating water and is separated from the water, the water is recycled and the evaporated water is replaced by feed water.
2. Discussion of Prior Art
It is known to produce synthesis gas containing hydrogen and oxides of carbon by cracking hydrocarbons with steam at temperatures above 700.degree. C. in the presence of an indirectly heated, nickel-containing catalyst. It is further known to form methanol by reacting the synthesis gas under pressures of 30 to 80 at temperatures of 230.degree. to 280.degree. C. in the presence of a copper-containing catalyst, contained in a reactor in tubes which are indirectly cooled with water. It is also known to utilize the cooling of the reactor tubes for production of high-pressure steam (German Pat. No. 20 13 297).
A known apparatus for producing methanol in another process comprises a tubular reactor having tubes contacted by flowing boiling water under pressure. In that apparatus, the feed water enters the lower part of the reactor and the resulting stream is fed to a super-heater. Part of that steam can be withdrawn as high-pressure steam and another part can be supplied to a turbine, which drives a compressor. The remaining part of the steam can be recovered as turbine steam (German Pat. No. 21 23 950).
In the operation of the previously known tubular reactor, circulating water from a steam header is fed to the tubular reactor. Part of the fed water is evaporated at the catalyst-filled tubes, in which the components H.sub.2 O, CO and CO.sub.2 are reacted to form methanol. By thermosiphon action, the resulting steam together with circulating water is forced into the steam header, where the steam is separated whereas the water, which is at its boiling point is returned to the lower part of the reactor. The steam withdrawn from the steam header must be returned to the system as feed water. Depending on the preheating of that feed water the temperature in the steam header will be more or less close to the boiling point of water. If the water is circulated about ten times, feed water is fed at a temperature of 120.degree. C. and a pressure of 40 bars is maintained in the system, the circulating water fed to to the lower part of the reactor will be at a temperature of about 237.degree. C., which is 13.degree. C. under its boiling point. As a result, the temperature difference at the lower part of the reactor tubes containing catalyst at a temperature of about 255.degree. C. is very low and precludes an appreciable heat exchange and a cooling of the reacting mixed gases in the tubes.
Only steam at a pressure up to about 40 bars can be produced in the known tubular reactors for producing methanol because the copper catalyst is susceptible to elevated temperatures and a good equilibrium control is desired.
It is an object of the invention to avoid these disadvantages of the state of the art and to obtain a higher temperature difference in the lower part of the reactor and to effect an improved and more intense cooling of the reacting mixed gases. The equilibrium control is to be improved and steam under higher pressure is to be produced at the same time. The process should involve lower energy costs.
This object is accomplished according to the invention in that a perforated thin intermediate bottom plate is provided, which is spaced 20 to 150 cm over the lower tube plate, the reactor is fed with the circulating water above that intermediate bottom and with the feed water below that intermediate bottom, the gaseous reaction mixture is cooled by 20.degree. to 50.degree. C. in the lower part of the catalyst-filled tubes in a tube length of 20 to 150 cm, the feed water is heated in the reactor to temperatures of 230.degree. to 290.degree. C. with evaporation of part of the feed water, the resulting mixture of steam and circulating water is separated, the circulating water is recycled and the resulting high-pressure steam is withdrawn.
In accordance with the invention the intermediate bottom is suitably spaced 50 cm over the lower tube plate.
The circulating water fed to the reactor is desirably at a temperature of 200.degree. to 300.degree. C., preferably at a temperature of 230.degree. to 290.degree. C., and the feed water is fed at a temperature of 100.degree. to 180.degree. C., preferably 110.degree. to 150.degree. C.
The advantages afforded by the invention reside particularly in that the temperature difference between the cooling fluid and the catalyst contained in the tubes can be increased in the lower part of the reactor in a simple, energy-saving process. As a result, the heat exchange is increased and the reacting gas mixture is cooled to a lower temperature so that the thermodynamic equilibrium is promoted. The temperatures used are within the limits determined by the recrystallizating characteristics of the catalyst. Methanol can be produced more economically in accordance with the invention.